This invention relates generally to a permeable membrane method and apparatus for the separation of liquids and, more particularly, to such a method and apparatus for purifying blood in the absence of a functional kidney for that purpose.
Permeable membrane elements are used in a wide variety of devices in which the different components of multi-component fluids are to be resolved. Many types of permeable membranes have been developed including osmotic membranes, ion exchange membranes, those that possess selective permeation rates for two or more non-ionic components of fluid mixtures and, of particular interest in this invention, the so-called molecular sieve type membranes that accommodate dialysis in devices such as artificial kidneys. Although they function effectively to separate fluids, membrane devices exhibit an inherent disadvantage of accommodating only slow rates of diffusion. For this reason developers in the field have sought membrane geometries that yield high membrane surface-to-volume ratios.
One known high membrane surface-to-volume ratio device utilizes a bundle of hollow capilary fibers within a shell. A feed mixture is introduced into the open ended fibers at one end of the bundle, a permeate-lean fraction is removed from the open ended fibers at the opposite end of the bundle, and a permeate-rich fraction is removed with a sweep stream that flows between the shell and the fibers. Separatory devices of this type are disclosed, for example, in U.S. Pat. Nos. 3,019,853; 3,228,877; 3,536,611 and 3,708,071. Although exhibiting high membrane surface-to-volume ratios, the fiber bundle separatory devices generally exhibit the disadvantage of causing non-uniform flow and channeling of the sweep stream and a poor fluid flow distribution pattern that results in a reduction in separatory efficiency. The poor fluid flow patterns result primarily from capilary action that draws the individual fibers of the bundle closely together thereby inhibiting flow and preventing uniform wetting thereof.
The object of this invention, therefore, is to provide a hollow fiber bundle type separatory device that exhibits improved fluid flow characteristics and more uniform wetting of the available membrane surface.